This invention relates in general to processes for forming semiconductor devices, and more particularly to processes for forming semiconductor devices including interconnect barrier layers.
Forming conductive bumps over semiconductor device bond pads is becoming increasingly common as the sizes and packages of the semiconductor devices continue to shrink. The bumps are used instead of wires to electrically connect the bond pads to their respective packaging leads. One specific type of bump includes a controlled-collapse chip-connection (C4) bump. Bumps generally require that a pad limiting metal layer be formed between the bond pad and the bump. Pad limiting metal layers typically include chrome and chromium alloys. However, these chromium-containing films can have defects, such as cracks and irregular grain boundaries, which limit the ability of the chromium layer to adequately separate the bond pad and the bump materials.
The bump typically includes elements such as tin (Sn) and lead (Pb). In the event the barrier fails to keep the bond pad and the bump separated, material from the bond pad can react with the lead or tin in the bump and intermetallic alloys of these materials can be formed. If the bond pad includes a copper-containing material, a brittle intermetallic alloy can be the result. The brittle intermetallic alloy can subsequently crack and result in bump failure. In addition, voids can form as a result of the alloying process and degrade adhesion between the bond pad and the bump. In extreme cases this can produce high resistance that can negatively impact the semiconductor device""s performance and even result in failure of the semiconductor device.